I am going to guess that I am probably the senior boot user here. I have been using hoof boots almost nonstop since 1979, when the REAL original EasyBoots were pretty new on the market, have used several and watch new introductions with great interest. So when this boot caught my eye, it looked like a really fresh, new concept. For many of my boot-using years, the EasyBoot was the only show in town. Easycare has grossly cheapened their products over the years, and I feel that they keep trying to reinvent the wheel by slapping new uppers on the same old sole, never innovating a boot for hind hooves or trialing new materials. I've had a pair of Chinese made EasyBoots sit on a shelf for a year and had the sidewalls become brittle and cracked. Gaiters are constantly ripping, or being redesigned. (I have a horse that can pop right out of a pair of Epics without even opening the gaiters up!) The new Fury Slings and Hearts are not receiving very good reviews, the Glove is purported to be best when heat fitted and requires a perfect fit. The gaiters on most EasyCare boots rip prematurely and the cables of EasyBoots and Renegades are notorious for breaking. The ones on Epics are too hard for my old hands to open now. (On Easyboots, the stock cables can be replaced with stainless steel from Home Depot and installed with ferrules for wire rope - just buy some and cut to length.)
Velcro is the nemesis of Cavallo boot users. Cavallos, Old Macs and Back Country's are extremely bulky and heavy. The Back Country is a gutted and plasticized version of the Old Macs with very flimsy gaiter material at the back. I had a horse practically destroy the protruding fasteners in one drive. Scoots require an extremely good fit, Renegades have the usual Velcro and cable breakage problems. Evos seem to have a lot of breakable parts.
There probably isn't a boot that will stay on under all circumstances, that will never twist or rub. I admit, I've been sore tempted to try composite shoes. There are certainly as many drawbacks that can be mounted for steel shoes as boots, if one cared to wade into that debate!
I put my money out for the Flex boots with a lot of trepidation, but I am seriously after a lightweight boot, that isn't going to bog down my mare's way of going, as she seems sensitive to that sort of thing. These boots look to me as if they'll be more forgiving of her less-than-perfect heels and the small amount of feedback I've found on them has been positive. I actually don't think they'll rub. The gaiters are neoprene, which is what I use in Cavallos to prevent rubbing. I like that they're not made in China!
I use boots because originally I felt, and still do, that they are a superior choice for DRIVING horses working on pavement, which is what I did for 40 years, and never had a lameness. I no longer drive, but I now have other reasons to continue using them.
If they don't work, I can pass them on and fall back on my current boots of choice, which have performed unfailingly, but I judge are too heavy. But if they do work, won't I be grinning like the Cheshire cat!